1. Field of the Invention
This invention relates to a semiconductor memory device and to a technique which will be effective when utilized for a nonvolatile semiconductor memory device, such as an EPROM (Erasable & Programmable Read-Only Memory), which is capable of writing data electrically.
2. Description of the Related Subject Matter
The data write operation in an EPROM comprises designating an address, inputting information data to be written, setting the operation mode thereof to a write mode by an externally applied control signal and writing information data into a selected memory cell. When the write operation is completed, the operation mode is then set to a verify (read) mode by an externally applied control signal. That is, the memory cell at the address described above into which the write operation is made is read out and a write confirmation is made by a writing device (EPROM writer) between the information data to be written and the information data that is read out. Such an EPROM is described, for example, in the publication, "Hitachi IC Memory Data Book," June 1987, pps. 489-603.
In conventional EPROMs the operation mode is designated by externally applied control signals, as described above. Therefore, if the write operation is attempted from a microprocessor or the like under the state where the EPROM is assembled in a microcomputer system (on-board state), the microprocessor itself must continue to generate the external control signal described above, for the write mode time period, although it needs a relatively long period. The inventors of the present invention have determined that in the interim, the operations of the microprocessor and the like are not fully or satisfactorily carried out resulting in the through-put of the system becoming extremely deteriorated.